In most high voltage d-c power supplies, a step-up transformer is employed as the conversion element from the low voltage source to the high voltage output. In d-c power supplies of this type, a relatively low voltage d-c source is applied to a d-c to a-c converter which converts the d-c power to an alternating current which is applied to the primary winding of the step-up transformer. The a-c current in the primary winding of the transformer induces a relatively high voltage a-c output across the secondary winding of the transformer. This a-c output is applied to an a-c to d-c converter and then to a load.
To obtain maximum power input to the load, the transformer parameters should be chosen so that the load impedance is equal to the magnitude of the equivalent Thevenin impedance as seen from the load terminals. Since maximum power transfer occurs with a power factor of 1, the Thevenin impedance is preferably the complex conjugate of the load impedance. When determining these parameters, capacitive losses in the transformer are normally ignored. The resulting parameters are usually satisfactory since the capacitive losses in the transformer are minimal for low power and low frequency applications. When utilizing a large step-up transformer wherein the turns ratio n=N.sub.p /N.sub.s is much less than 1, the capacitive losses have a significant effect on the equivalent Thevenin impedance as seen from the load terminal. As a result, the load to source voltage ratio is substantially reduced and substantially less power is available to the load.
The above-mentioned capacitive losses in the transformer are primarily due to inter-winding and inter-turn losses. The inter-turn capacitive losses exist within both the primary and second windings of the transformer. The parameters of these losses are determined by the location and spacing of the individual turns of the winding. The inter-winding losses appear between the secondary and primary windings and are also a function of the location and spacing of these windings. In both cases the value of the capacitive losses is affected by the dielectric constant of the material in which the windings are immersed. In most high voltage transformers, a potting compound having a high dielectric constant employed. As a result, the capacitive losses in these transformers are substantially increased.